1. Field of the Invention
The present invention relates to a keyless entry system, and in particular, a keyless entry system capable of reducing the influence of an interference wave.
2. Description of the Related Art
A keyless entry system which can perform vehicle operation, such as locking and unlocking of the doors of the vehicle, through radio communication between an on-vehicle unit mounted in a vehicle and a mobile device carried by a user of the vehicle without using a mechanical key has spread.
Typically, in the keyless entry system, the on-vehicle unit transmits a radio signal having a frequency (30 kHz to 300 kHz) in a low frequency (LF) band to the mobile device, and the mobile device transmits a radio signal having a frequency (300 MHz to 3 GHz) in an ultrahigh frequency (UHF) band to the on-vehicle unit corresponding to the radio signal having a frequency in the LF band, whereby radio communication can be performed between the on-vehicle unit and the mobile device. Then, a wakeup signal for activating a predetermined function of the mobile device is radio-transmitted from the on-vehicle unit to the mobile device through radio communication between the on-vehicle unit and the mobile device, and a command signal relating to vehicle operation is radio-transmitted from the mobile device to the on-vehicle unit corresponding to the wakeup signal. In the keyless entry system, in this way, on-vehicle equipment, such as a door locking device, is controlled using the wakeup signal radio-transmitted from the on-vehicle unit to the mobile device and the command signal radio-transmitted from the mobile device to the on-vehicle unit corresponding to the wakeup signal, thereby performing vehicle operation, such as locking and unlocking of the doors of the vehicle.
On the other hand, when the mobile device of the keyless entry system is carried along with another electronic apparatus, such as a mobile information terminal, an interference wave (noise) in an LF band generated from a display device, a drive circuit, or the like of the electronic apparatus affects the mobile device, and may interfere with the reception of the radio signal in the LF band radio-transmitted from the on-vehicle unit. Then, the mobile device cannot normally receive the radio signal in the LF band due to the influence of the interference wave generated by the electronic apparatus, and the on-vehicle unit may not reliably transfer the wakeup signal to the mobile device. For this reason, it is possible to reduce the influence of the interference wave generated by another electronic apparatus.
As a keyless entry system capable of reducing the influence of the interference wave generated by another electronic apparatus, a passive keyless entry device (keyless entry system) described in Japanese Unexamined Patent Application Publication No. 2006-16928 or the like has been suggested. FIGS. 7A and 7B are explanatory views showing the configuration of a passive keyless entry device 100 described in Japanese Unexamined Patent Application Publication No. 2006-16928. FIG. 7A shows an on-vehicle transceiver 110 (on-vehicle unit) and FIG. 7B shows a mobile transceiver 120 (mobile device).
As shown in FIGS. 7A and 7B, the passive keyless entry device 100 described in Japanese Unexamined Patent Application Publication No. 2006-16928 includes the on-vehicle transceiver 110 and the mobile transceiver 120. In the passive keyless entry device 100, a first transmission signal including a wakeup signal is radio-transmitted from the on-vehicle transceiver 110, if the mobile transceiver 120 receives the first transmission signal, a second transmission signal including a command signal is radio-transmitted from the mobile transceiver 120, and the on-vehicle transceiver 110 which receives the second transmission signal controls a controlled apparatus (on-vehicle equipment) based on the command signal.
The on-vehicle transceiver 110 has a low frequency signal transmitter 101, a transmission low frequency antenna 102, a high frequency signal receiver 103, a reception high frequency antenna 104, a controller 105, a low frequency oscillator 106, a drive signal transmitter 107, and a storage unit 108. The low frequency signal transmitter 101 radio-transmits the first transmission signal (low frequency signal) including the wakeup signal to the mobile transceiver 120 through the transmission low frequency antenna 102. The high frequency signal receiver 103 receives the second transmission signal from the mobile transceiver 120 through the reception high frequency antenna 104. The controller 105 controls various circuits of the on-vehicle transceiver 110.
The mobile transceiver 120 has three signal reception circuits 121 each having an antenna 127 and an amplifier 128, a pattern comparator 122, a selector circuit 123, a storage unit 124, a counter 125, an AND gate 126, an adder 129, and a detector 130. The three signal reception circuits 121 respectively receive signal components in three orthogonal directions in the first transmission signal. The adder 129 and the detector 130 output a detection signal corresponding to an output signal of each of the three signal reception circuits 121. The pattern comparator 122 and the storage unit 124 perform the detection of the wakeup signal on the detection signal corresponding to the output signal of each of the three signal reception circuits 121.
Then, when the wakeup signal is normally detected (when the first transmission signal could be normally received), the mobile transceiver 120 radio-transmits the second transmission signal including the command signal using transmission means (not shown). When the detection signal from which the wakeup signal cannot be normally detected is obtained (when the first transmission signal could not be normally received), the selector circuit 123 places the signal reception circuit 121 deriving the detection signal in a non-operation state.
In this way, in the passive keyless entry device 100, the three signal reception circuits 121 respectively receive the signal components in the three orthogonal directions in the first transmission signal, thereby receiving the first transmission signal in a direction other than the direction in which the interference wave is generated. Accordingly, it is possible to reduce the influence of the influence wave. When the selector circuit 123 places the signal reception circuits 121, which cannot normally receive the signal components of the first transmission signal, in a non-operation state, thereby suppressing an increase in power consumption of the mobile transceiver 120 accompanied by reduction in the influence of the interference wave.
However, in the passive keyless entry device 100 described in Japanese Unexamined Patent Application Publication No. 2006-16928, a countermeasure against an interference wave is provided only based on whether or not the wakeup signal could be normally detected, that is, whether or not the first transmission signal could be normally received, and it is not necessarily true that the presence/absence of the interference wave or the incoming direction of the interference wave is detected. For this reason, when the interference wave to the first transmission signal is present around the mobile device, and all signal reception circuits 121 could not normally receive the signal components of the first transmission signal, it is not possible to provide an effective countermeasure against an interference wave, and it may not be possible to reliably transfer the wakeup signal.